Nearsightedness with or without astigmatism is an ocular condition wherein the image of distant objects is formed in front of the retina. Here, light is focused in front of the retina of the myopic eye, and, in most cases, this is due to the fact that the eye is too large from front (corneal) to back (axial).
There are two types of myopia: majority of patients have a step cornea and others have extreme myopia caused by a long eyeball.
What then is astigmatism?
It is a condition wherein the steepness of the cornea is not even and is comparable to the shape of a football. On the other hand, no astigmatism is shaped like a basketball. In effect, astigmatism causes blurring of the vision from afar and clearer vision at a near distance.
However, the opposite is true in farsighted individuals or those suffering from hyperopia. The image of distance objects is formed behind the retina because the eye is too short. Here, light is focused behind the retina in the hyperopic eye.
For others, there is presbyopia wherein an individual has difficulty reading at a near distance when approaching the age of 40. This is due to loss of the accommodative power of the eye, brought about by weakness of the muscles inside the eye.
Studies have shown that errors of refraction in myopia and hyperopia represent anomalies of development. In myopia, the eye grew too much after birth and in hyperopia, it grew too little.
The environment plays a role in the development of myopia. This has been shown in studies wherein the level of myopia increased with the advent of electricity in an Eskimo study.
Furthermore, myopia increases as the level of education increases. Prolonged work in predisposed children and adolescents may cause myopia through excessive accommodation.
The prevalence of myopia in the Philippines is not fully known, as we do not have a national registry for this kind of ocular condition. Some studies may single out a particular subset of the population but not at the national level. In a recent survey at the Philippine General Hospital, the prevalence of ammetropias is about 25 percent.
In lieu of this, our bases of prevalence will be other Asian countries. However, in Singapore, the prevalence of myopia is 43.3 percent. Myopia is 15.4 percent prevalent among males with no formal education and increases steadily through the education levels to reach 65.1 percent, among university graduates in 1987-1991.
In a Hong Kong study, among 383 school children from ages 6 to 17, the prevalence of myopia increased from 30 percent at ages 6-7 to 70 percent at ages 16-17.
In the Hong Kong Polytechnic University, the prevalence of myopia was 75 percent among females and 69 percent among males. In Taiwan, the prevalence of myopia is over 70 percent, according to the national survey of children there.
Among university medical students, the prevalence of myopia increased from 92.8 to 95.8 percent over a five-year period. In 1999, around 34 percent of Singaporean children between the ages of 7 and 9 suffered from myopia.
In the United States, the prevalence of myopia is about 25 percent (low myopia, 43 percent; moderate myopia, 3.2 percent; and high myopia, 0.2 percent), but in Asian countries such as China and Japan, it may exceed 70 percent, and it is approximately 90 percent in selected populations such as the Chinese university students.
For patients who are candidates for laser treatment, there are two options: Lasik (Laser-in-situkeratomileusis) and PRK (photorefractive keratectomy). Both procedures will not correct presbyopia, hence individuals who are 40 years old and above may require reading glasses.
St. Luke’s Vision Laser Center, which is staffed by US-trained and certified surgeons, is well-equipped for advanced treatment of myopia, astigmatism and hyperopia. It does all types of refractive surgery from Lasik, PRK, phakic lens implantation and astigmatic keratotomy. It’s a one-stop center for all eye problems.
Zyoptix is Bausch and Lomb’s state-of-the-art, personalized or custom-tailored Lasik, which utilizes the following instruments: Orbscan II (for computerized mapping of the cornea), aberrometer (which measures the total optical aberration of the eye) and 217 Z excimer laser.
Candidates for Lasik need to undergo a screening process, which includes a complete eye examination and the use of the mentioned instruments. Those who wear contact lenses are required to remove their lenses three days (soft contact) to two weeks (hard contact) prior to examination. The screening process for the Zyoptix is about one and a half hours. Zyoptix enables the individual to see better than 20/20 after Lasik.
Needless to say, strict compliance with post-operative instructions is very important. Things like rubbing the eye or wetting it with water should be avoided within the immediate post-operative period. Swimming in fresh water or pools is not allowed for a month.
Now, greeting friends and loved ones need not be a problem. Peering through a magnifying glass just to recognize them is no longer necessary.
(The author is with the St. Luke’s Vision Laser Center. He trained with the New England Eye Center of Tufts University in 1995-1996 and later joined Cornea Consultants affiliated with Harvard Medical School in 1996.)